Infection by the HCV is a compelling human medical problem and is now recognized as the causative agent for most cases of non-A, non-B hepatitis.
The HCV is thought to infect chronically 3% of the world's population [A. Alberti et al., “Natural History of Hepatitis C,” J. Hepatology, 31, (Suppl. 1), 17-24 (1999)]. In the United States alone the infection rate is 1.8% or 3.9 million people [M. J. Alter, “Hepatitis C Virus Infection in the United States,” J. Hepatology, 31, (Suppl. 1), 88-91 (1999)]. Of all patients infected over 70% develop a chronic infection that is believed to be a major cause of cirrhosis and hepatocellular carcinoma. [D. Lavanchy, “Global Surveillance and Control of Hepatitis C,” J. Viral Hepatitis, 6, 35-47 (1999)]
The replication of the HCV encompasses genomic encoding a polyprotein of 3010-3033 amino acids [Q.-L. Choo, et al., “Genetic Organization and Diversity of the Hepatitis C Virus”, Proc. Natl. Acad. Sci. USA, 88, 2451-2455 (1991); N. Kato et al., “Molecular Cloning of the Human Hepatitis C Virus Genome From Japanese Patients with Non-A, Non-B Hepatitis”, Proc. Natl. Acad. Sci. USA, 87, 9524-9528 (1990); A. Takamizawa et al., “Structure and Organization of the Hepatitis C Virus Genome Isolated From Human Carriers”, J. Virol., 65, 1105-1113 (1991)]. The HCV nonstructural (NS) proteins are presumed to provide the essential catalytic machinery for viral replication. The NS proteins are derived by proteolytic cleavage of the polyprotein [R. Bartenschlager et al., “Nonstructural Protein 3 of the Hepatitis C Virus Encodes a Serine-Type Proteinase Required for Cleavage at the NS¾and NS⅘Junctions”, J. Virol., 67, 3835-3844 (1993); A. Grakoui et al. “Characterization of the Hepatitis C Virus-Encoded Serine Proteinase: Determination of Proteinase-Dependent Polyprotein Cleavage Sites”, J. Virol., 67 2832-2843 (1993); A. Grakoui et al., Expression and Identification of Hepatitis C Virus Polyprotein Cleavage Products”, J. Virol., 67, 1385-1395 (1993); L. Tomei et al., “NS3 is a serine protease required for processing of hepatitis C virus polyprotein”, J. Virol., 67, 4017-4026 (1993)]. In fact, it is the first 181 amino acids of NS3 (residues 1027-1207 of the viral polyprotein) have been shown to contain the serine protease domain of NS3 that processes all four downstream sites of the HCV polyprotein [C. Lin et al., “Hepatitis C Virus NS3 Serine Proteinase: Trans-Cleavage Requirements and Processing Kinetics”, J. Virol., 68, 8147-8157 (1994)].
The HCV NS protein 3 (NS3) contains a serine protease activity that helps in the processing of the majority of the viral enzymes, and thus is considered essential for viral replication and infectivity. The essentiality of the NS3 protease was inferred from the fact that mutations in the yellow fever virus NS3 protease decreases viral infectivity [T. J. Chambers et al., “Evidence that the N-terminal Domain of Nonstructural Protein NS3 From Yellow Fever Virus is a Serine Protease Responsible for Site-Specific Cleavages in the Viral Polyprotein”, Proc. Natl. Acad. Sci. USA, 87, 8898-8902 (1990)]. More recently, it was demonstrated that mutations at the active site of the HCV NS3 protease could completely abolish the HCV infection in a chimpanzee model [C. M. Rice et al. “Hepatitis C virus-encoded enzymatic activities and conserved RNA elements in the 3′-nontranslated region are essential for virus replication in vivo.” J. Virol., 74(4) 2046-51 (2000)]. The HCV NS3 serine protease is also considered essential for viral replication as it and its associated cofactor, NS4A, help in the processing of all of the viral enzymes. This processing appears to be analogous to that carried out by the human immunodeficiency virus (“HIV”) aspartyl protease. In addition, the demonstrated use of HIV protease inhibitors as potent antiviral agents in man demonstrates that interrupting a protease protein processing stage in the viral life cycle does result in therapeutically active agents. Consequently, the protease enzyme is an attractive target for drug discovery.
Several potential HCV protease inhibitors have been described. PCT Publications Numbers WO 00/09558, WO 00/09543, WO 99/64442, WO 99/07733, WO 99/07734, WO 99/50230, WO98/46630, WO 98/17679 and WO 97/43310, U.S. Pat. No. 5,990,276, M. Llinás-Brunet et al., Bioorg. Med. Chem. Lett., 8, 1713-1718 (1998), W. Han et al., Bioorg. Med. Chem. Lett., 10, 711-713 (2000), R. Dunsdon et al., Bioorg. Med. Chem. Len., 10, 1571-1579 (2000), M. Llinás-Brunet et al., Bioorg. Med. Chem. Lett., 10, 2267-2270 (2000), and S. LaPlante et al., Bioorg. Med. Chem. Lett., 10, 2271-2274 (2000) each describe potential HCV NS3 protease inhibitors. Unfortunately, there are no serine protease inhibitors available currently as anti-HCV agents.
In fact, there are no anti-HCV therapies except interferon-α, interferon-α/ribavirin combination and more recently pegylated inteferon-α. The sustained response rates for the interferon-α therapies and interferon-α/ribavirin however tend to be low (<50%) and the side effects exhibited by the therapies tend to be significant and severe [M. A. Walker, “Hepatitis C Virus: an Overview of Current Approaches and Progress,” DDT, 4, 518-529 (1999); D. Moradpour et al., “Current and Evolving Therapies for Hepatitis C,” Eur. J. Gastroenterol. Hepatol., 11, 1199-1202 (1999); H. L. A. Janssen et al., “Suicide Associated with Alfa-Interferon Therapy for Chronic Viral Hepatitis,” J. Hepatol., 21, 241-243 (1994); and P. F. Renault et al., “Side effects of alpha interferon”, Seminars in Liver Disease 9, 273-277, (1989)]. Furthermore, the interferon therapies only induce long term remission in only a fraction (˜25%) of cases [O. Weiland, “Interferon Therapy in Chronic Hepatitis C Virus Infection”, FEMS Microbiol. Rev., 14, 279-288 (1994)]. The aforesaid problems with the interferon-α therapies has even led to the development and clinical study of pegylated derivatized interferon-α compounds as improved anti-HCV therapeutics.
In view of the current situation regarding anti-HCV therapeutics, it is clear that there is a need for more effective and better tolerated therapies.
Furthermore, synthesis of complex peptidomimetic compounds has long been hampered by the nonstereoselective nature of most synthetic organic processes. It is well known that the therapeutic activity of enantiomers of peptidomimetic compounds varies widely. It is therefore of great benefit to provide such stereospecific synthetic processes.
Previous attempts to synthesize chirally specific bicycloprolinate intermediates, useful in the synthesis of the present therapeutic peptidomimetic protease inhibitors have suffered from being non enantioselective, or diastereoselective, or long encompassing synthetic pathways, or being unsuitable for preparing large quantities of product. Thus, there is also a need for a means of preparing large quantities of bicycloprolinates in a diastereoselective manner and enantiomerically enriched form.